Controlled catalytic converter heating

ABSTRACT

The rate at which a catalytic converter for an internal combustion engine heats up to its normal operating temperature range can be increased by applying an electrical load that is powered by the internal combustion engine. Applying the electrical load demands more power from the engine which therefore has to work harder to maintain a given engine speed. The internal combustion engine then generates more heat that can be used to reduce the time to bring the catalytic converter up to its working temperature. The electrical load can be a catalytic converter heater to further reduce the time to bring the catalytic converter up to its working temperature. The result is a reduction in emissions.

BACKGROUND

1. Field

Example embodiments of the invention relate to controlling heating of a catalytic converter.

2. Related Art

A significant proportion of the emissions from a modern automotive internal combustion engine occurs during the first few minutes of the engine operation following a cold start. This is due to the catalytic converter not being able to function correctly until it achieves “light off”, that is until it has reached its working temperature.

A catalytic converter can be very effective at reducing unwanted exhaust emissions when it is operating at its working temperature. However, until a catalytic converter reaches its working temperature, it works inefficiently at best. As a result, untreated exhaust gas can exit the end of the exhaust, or tailpipe. In the first two to three minutes of warm-up following a cold start, about 60% to 80% of exhaust, or tailpipe, emissions occur.

The regulatory authorities are imposing ever more strict emission regulations. In order to provide an effective reduction in exhaust emissions, it is therefore desirable to cause the catalytic converter to get up to working temperature as quickly as possible.

Various approaches have been employed to reduce the time that it takes a catalytic converter to reach its working temperature. One approach is to moving the catalytic converters as close to the exhaust ports as possible. A further approach that has been suggested is to provide an exhaust gas combustion system. A further approach is to provide a mechanism to retain the heat in a catalytic converter between journeys. All of these approaches involve expensive modifications to an existing engine system and/or exhaust system and/or provide packaging challenges.

It has also been suggested to provide electrical and/or flame heaters for catalytic converters, although this has not been done in an integrated manner.

Other engine based approaches include providing precise fuelling control, providing controlled ignition retarding, providing secondary air injection, using high starting engine speed and providing changes to the catalyst physics. These approaches include various disadvantages including a less enjoyable driving experience (e.g. due to increased noise), reductions in performance, complexity, combustion stability and cost.

Accordingly, there is still a need for an improved solution to reduce the time taken for a catalytic converter to reach its working temperature.

SUMMARY

An example embodiment of the invention can provide a method of operating an engine system. The engine system can include an internal combustion engine that is operable to apply drive to a drive train, a catalytic converter through which exhaust gases from the internal combustion engine pass and a control system. The method can include the control system determining whether the internal combustion engine is in an operating phase in which the catalytic converter is not at its working temperature. In response to such a determination by the control system, the control system can activate an electrical load element that is powered by the internal combustion engine whereby an additional load is placed on the internal combustion engine.

By activating an electrical load element that is driven by the internal combustion engine, the internal combustion engine has to work harder to maintain a give engine speed and therefore generates more heat that can be used to reduce the time that it takes to bring the catalytic converter up to its working temperature. As a result, a reduction in emissions can be achieved.

In an example embodiment the electrical load is a catalytic converter heater. In this case, there is the added benefit that the catalytic converter heater is also working to increase the temperature of the catalytic converter, which has the effect of further reducing the time that it takes to bring the catalytic converter up to its working temperature and further reducing emissions.

An embodiment of the invention can provide an engine system. The engine system can include an internal combustion engine that is operable to apply drive to a drive train, a catalytic converter through which exhaust gases from the internal combustion engine pass and a control system. The control system can be operable to determine whether the internal combustion engine is in an operating phase in which the catalytic converter is not at its working temperature and, if so, to activate an electrical load element that is powered by the internal combustion engine, whereby an additional load is placed on the internal combustion engine.

A motor vehicle can be provided with such an engine system. The electrical load can be in the form of a catalytic converter heater. The operating phase operating phase of the internal combustion engine can be a start up phase.

The motor vehicle can be a hybrid vehicle that also includes at least one electric drive motor. The operating phase of the internal combustion engine can be one of a start up phase and an electrical drive phase.

BRIEF DESCRIPTION OF THE FIGURES

Specific example embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings.

FIG. 1 is a chart illustrating an example of emissions during phases of operation of an engine system.

FIG. 2 is a chart illustrating accumulated emissions during operation of an engine system.

FIG. 3 is a schematic representation of a motor vehicle including an engine system.

FIG. 4 is a schematic representation of an engine system.

FIG. 5A is a schematic representation of the operation of an engine system during normal running or operation.

FIG. 5B is a chart showing various parameters of the engine system during normal running or operation.

FIG. 6A is a schematic representation of the operation of a prior art engine system in a start up phase.

FIG. 6B is a chart showing various parameters of the prior art engine system in a start up phase.

FIG. 7A is a schematic representation of the operation of an example engine system in accordance with an example embodiment of the invention in a start up phase.

FIG. 7B is a chart showing various parameters of the example of an engine system in accordance with an example embodiment of the invention in a start up phase.

FIG. 8 is an example of a hybrid vehicle including an engine system as shown in FIG. 4.

FIG. 9 is a chart comparing an example of catalytic converter temperatures over time.

FIG. 10 is a chart illustrating an example of an improvement in the increase of catalytic converter temperature over time.

DETAILED DESCRIPTION

An example embodiment of the invention seeks to increase the rate at which a catalytic converter heats up to its normal operating temperature range by applying an electrical load that is powered by an internal combustion engine during a start up phase. Applying the electrical load demands more power from the engine which therefore has to work harder to maintain a given engine speed. The internal combustion engine therefore generates more heat that can be used to reduce the time to bring the catalytic converter up to its working temperature. As a result, a reduction in emissions can be achieved.

FIG. 1 is a chart illustrating an example of emissions during phases (e.g., during vehicle speeds VSpd) of operation of an engine system.

FIG. 1 illustrates an example of the emissions of an internal combustion engine, for example a gasoline engine, over time from a cold start. As can be seen in the circled portions of FIG. 1, high emissions are seen in the phase after start-up.

FIG. 2 represents the accumulative emissions of gases such as hydrocarbons (HC), nitrogen oxides (NO_(x)) and carbon dioxide (CO₂). It can be seen from the circled portions of the charts in FIGS. 1 and 2 that a significant proportion of the undesired emissions occur during the early start up phase. This is the phase before the catalytic converter has heated up to its normal operating temperature range and in which the catalytic converter is ineffective or at least less effective. The time that the catalytic converter takes to get up to its normal operating temperature range is often called the “light off time”.

Various approaches mentioned in the background above have been employed to reduce the light off time. However, the prior approaches all include disadvantages. An example embodiment of the invention can provide an improved engine system and method of operation thereof.

FIG. 3 is a schematic representation of a motor vehicle 10 including an engine system 12. In FIG. 3, the motor vehicle is an automobile and the engine system includes an internal combustion engine 14 with a drive train 16 driving the driven wheels 18. In the present example, the vehicle 10 has rear wheel drive. However, it will be appreciated that in other examples front wheel drive or all wheel drive can be provided. In the present example the drive train 16 is understood to include the transmission 20. The transmission 20 can be a manual or an automatic transmission.

FIG. 4 is a schematic representation of an example of an engine system 12 in accordance with an example embodiment of the invention for use, for example in the vehicle illustrated in FIG. 3.

As shown in FIG. 4, the internal combustion engine 14 is provided with an air intake system 22 and an exhaust system 24 including an exhaust pipe, or tail pipe 23. The exhaust system 24 includes a catalytic converter 25 for processing the exhaust gases.

A control system 26 includes an engine management controller 28 that is responsive to various sensors, including one or more lambda probes 30, one or more catalytic converter temperature sensors 32, and one or more ambient temperature sensors 34, one or more crankshaft sensors 36, etc. In an example embodiment, the control system is also operable to control the automatic transmission 20, braking systems (not shown in FIG. 4) and other systems as well as controlling engine parameters such as ignition timing, fuel injection timings and so on.

The engine system 12 further includes a battery 40 that is used to provide electrical power electrical components of the engine system via a regulator 42. The battery is kept charged by means of a generator 44 that is driven by the internal combustion engine, for example via a drive belt or drive chain.

In this example embodiment of the invention, the catalytic converter is provided with a catalytic converter heater 45. In FIG. 4, the catalytic converter heater 45 is shown schematically as a resistive element. The catalytic converter heater 45 can be provided in any appropriate form. For example, the catalytic converter heater 45 can be provided externally to the catalytic converter 25, for example in the form of a jacket for the catalytic converter 25. Alternatively, the catalytic converter heater 45 can be provided integrally to the catalytic converter 25. For example, the catalytic converter 25 can be provided with resistive plates forming a carrier for the catalyst in the catalytic converter.

The control system 26 can be responsive to sensors (not shown) to determine if the internal combustion engine is in an operating phase in which the catalytic converter is not at its working temperature. In such a case, the control system 26 can activate the catalytic converter heater 45 to heat the catalytic converter 25. The catalytic converter heater forms an electrical load element that is powered by the internal combustion engine via the generator 44, either directly, or for example via the regulator 42 as shown in FIG. 4, or via another route. The regulator 42 and/or the control system 26 can be operable to ensure that power for the catalytic converter heater 45 is taken from the generator rather than from the battery 40. For example, the power required by the catalytic converter heater can be such that it is greater than the power that can be supplied by the battery 40. However in any case, the aim is to cause the internal combustion engine to work harder (i.e., produce more power) in order that additional heat generated by the internal combustion engine working harder can be used to heat up the catalytic converter even more quickly than merely through the use of the catalytic converter heater 45 and/or the normal running of the engine. Thus, drawing power from the internal combustion engine 14 via the generator 44 causes an external load to be applied to the engine over an above the normal loading caused by internal friction, etc., and the internal combustion engine 14 has to work harder to maintain a given engine speed. The control system 26 can be operable to maintain the engine speed at a desired level to give smooth engine running under load by applying an appropriate amount of throttle.

As a result of the additional electrical load caused by the catalytic converter heater 45, the time for heating up the catalytic converter is reduced by the dual effects of the direct heating effect of the catalytic converter heater 45 and the additional load that is placed on the internal combustion engine, whereby the heat output of the internal combustion engine is increased for a given engine speed compared to the situation where the additional electrical load is not applied.

FIG. 5A is a schematic representation of the operation of an engine system in normal running or operation. FIG. 5A represents, schematically, the internal combustion engine 14, the engine output shaft 42 (e.g. the crankshaft, an extension thereof, or a further shaft driven by the crankshaft), the transmission 20, including a torque converter 44 and a gearbox 46 (or in the case of a manual transmission, a clutch 44 and a gearbox 46), and a transmission drive shaft 48.

FIG. 5B is a chart that represents, schematically, the conditions of various parameters including engine load, ignition retard, engine speed, throttle, external load and heat flux to the catalyst during normal running. It will be appreciated that FIG. 5B represents these conditions in a steady state situation. It will also be appreciated that in normal use, these parameters can be changed, for example during acceleration, deceleration, etc.

FIG. 6A is a schematic representation of the operation of a prior art engine system in a start up phase. FIG. 6A represents, schematically, the internal combustion engine 14, the engine output shaft 42 (e.g. the crankshaft, an extension thereof, or a further shaft driven by the crankshaft), the transmission 20, including a torque converter 44 and a gearbox 46 (or in the case of a manual transmission, a clutch 44 and a gearbox 46), and a transmission drive shaft 48.

FIG. 6B is a chart that represents, schematically, the conditions of various parameters including engine load, ignition retard, engine speed, throttle, external load and heat flux to the catalyst during an example of operation of the prior art engine system during a start up phase. FIG. 6B illustrates that at an activation point, various parameters are changed. Specifically, it will be noted that after ignition (where the ignition trace drops) the throttle is increased, which also increases the engine speed and engine load caused by internal engine factors such as friction, etc. As a result, heat flux to the catalytic converter increases to start to heat the catalytic converter. Once again, it will be appreciated that FIG. 6B is schematic and is for illustrative purposes only.

FIG. 7A is a schematic representation of the operation of an engine system in accordance with an example embodiment of the invention during a start up phase. FIG. 7A represents, schematically, the internal combustion engine 14, the engine output shaft 42 (e.g. the crankshaft, an extension thereof, or a further shaft driven by the crankshaft), the transmission 20, including a torque converter 44 and a gearbox 46 (or in the case of a manual transmission, a clutch 44 and a gearbox 46), and a transmission drive shaft 48. FIG. 7A also illustrates, schematically, the application of an external load to the engine output shaft 42 by means of the hand 50. It will be appreciated that the representation of a hand 50 in FIG. 7A is merely to illustrate the effect of applying an additional electrical load in accordance with an example embodiment of the present invention. In practice, the load is not provided by a hand, but rather by activating an external electrical load.

FIG. 7B is a chart that represents, schematically, the conditions of various parameters including engine load, ignition retard, engine speed, throttle, external load and heat flux to the catalyst during an example of operation of an example embodiment of an engine system during a start up phase. FIG. 7B illustrates that at an activation point, various parameters are changed. Specifically, it will be noted that after ignition (where the ignition trace drops) the throttle is increased by a greater amount than in the prior art example of FIG. 6B, although the engine speed only increases by the same amount as in the prior art example of FIG. 6B. This is because an external electrical load is applied (see the lower circled portion in FIG. 7B), which means than the overall engine load is increased more (see the upper ringer portion in FIG. 7B) than in the prior art example of FIG. 6B. This is turn means that there is a greater heat flux to the catalytic converter (see the lower circled portion in FIG. 7B) than in the prior art example of FIG. 6B. Once again, it will be appreciated that FIG. 7B is schematic and is for illustrative purposes only. However, a comparison of FIGS. 6B and 7B illustrates the effect of applying the external electrical load to increase the heat flux to the catalytic converter and hence to reduce the light off time for the catalytic converter.

The external load can be applied until the catalytic converter has reached a predetermined temperature, for example a minimum efficient operating temperature, for a predetermined time, or a combination thereof (for example, until it has reached the predetermined temperature or until a predetermined time has elapsed, which ever occurs first). As will be seen in FIG. 10 below, a significant benefit can be realized though the use of the applied external load within the first ten seconds of operation. Accordingly, the external load could be applied merely for a predetermined period, for example twenty seconds, or ten seconds, or five seconds. The choice of a particular time to apply the load can also be dependent upon the amount of the loading that is applied. In general, the higher the loading, the shorter the time, although the loading should not be set such that it exerts excessive strain on the engine during the start up phase.

Where the additional electrical load is in the form of a catalytic converter heater, the time for heating up the catalytic converter is reduced by the dual effects of the catalytic converter heater and the additional load that is placed on the internal combustion engine, whereby the heat output of the internal combustion engine is increased for a given engine speed compared to the situation where the additional electrical load is not applied.

During operation of the engine system shown in FIG. 4, the control system 26 is operable to detect the activation point illustrated in FIG. 7B following ignition. This can be detected, for example, when ignition is achieved following a cold start of the engine or a start when the catalytic converter is not within its normal operating range of temperatures. The control system 26 is then operable automatically to activate the catalytic converter heater 45. As the catalytic converter heater 45 is powered by the internal combustion engine via the generator, this causes an external load to be applied to the engine over and above the normal loading caused by internal friction, etc., which means that the engine has to work harder to maintain a given engine speed. The control system 26 can be operable to maintain the engine speed at a desired level to give smooth running under load by applying an appropriate amount of throttle. The result of applying the additional external electrical load is that the light off time for the catalytic converter can be reduced compared to a prior art engine where an external load is not applied. Alternatively, the additional external load can enable the same amount of heating compared to a prior art engine where an external load is not applied, but at a reduced engine speed. As mentioned above, where the additional electrical load is in the form of a catalytic converter heater, the time for heating up the catalytic converter is reduced by the dual effects of the catalytic converter heater and the additional load that is placed on the internal combustion engine.

FIG. 8 is a schematic representation of an example of a hybrid vehicle 70 incorporating an engine system 12 in accordance with an example embodiment of the invention.

As shown in FIG. 8, an internal combustion engine 14 is provided with an air intake system 22 and an exhaust system 24. The exhaust system 24 includes a catalytic converter 25 for processing the exhaust gases and an exhaust pipe, or tail pipe 23 that includes one or more mufflers, or silencers, 27. The catalytic converter is provided with an electrically operated catalytic converter heater 45. In FIG. 8, the catalytic converter heater 45 is shown schematically as a resistive element. As discussed with reference to FIG. 4, the catalytic converter heater 45 can be provided in any appropriate form and can be separate from, or integral to, the catalytic converter 25.

In addition, and electric motor 64 and a generator 44 are provided. The internal combustion engine 14, the electric motor 64 and the generator 44 are coupled together via a power split device 66. The power split device 66 allows the vehicle to be powered by the electric motor 64 alone, the internal combustion engine 14 alone or by both together. The power split device 66 also allows internal combustion engine 14 to operate independently of the vehicle speed for charging batteries or providing power to the wheels 68 via the drive shafts 72 as needed. It also acts as a continuously variable transmission (CVT). The electric motor 64 can be coupled to the internal combustion engine 14 via the generator 44.

As mentioned, the control system 26 is responsive to various sensors (not shown). In an example embodiment, the control system is also operable to control the operation of the power split device and the generator and of the catalytic converter heater.

The vehicle further includes a battery 40 that is used to provide electrical power electrical components of the engine system via a regulator 42. The battery is kept charged by power supplied from the generator 44 that is driven by the internal combustion engine 14. Power for charging the battery 40 can also be provided through regenerative braking, solar power and other means.

In operation of the engine system of the vehicle shown in FIG. 8, the control system 26 is operable to detect the activation point illustrated in FIG. 7B following ignition. This can be detected, for example, when ignition is achieved following a cold start of the engine or a start when the catalytic converter is not within its normal operating range of temperatures. The control system 26 is then operable automatically to activate the catalytic converter heater 25. The power required by the catalytic converter heater 45 can be such that it is greater than the power that can be supplied by the battery 40. In such a case, the regulator 42 in combination with the control system 26 is operable to ensure that power for the catalytic converter heater 45 is taken from the generator 44 from power generated by the internal combustion engine 14. The effect of drawing the power from the internal combustion engine 14 via the generator 44 is to cause an external load to be applied to the engine over and above the normal loading caused by internal friction, etc., which means that the engine has to work harder to maintain a given engine speed. The control system 26 can be operable to maintain the engine speed at a desired level to give smooth engine running under load by applying an appropriate amount of throttle. The result of applying the additional external load is that the light off time for the catalytic converter can be reduced compared to a prior art engine where an external load is not applied. Alternatively, the additional external load can enable the same amount of heating compared to a prior art engine where an external load is not applied, but at a reduced engine speed.

As a result of the additional electrical load caused by the catalytic converter heater 45, the time for heating up the catalytic converter is reduced by the dual effects of the direct heating effect of the catalytic converter heater 45 and the additional load that is placed on the internal combustion engine, whereby the heat output of the internal combustion engine is increased for a given engine speed compared to the situation where the additional electrical load is not applied.

As described above, with reference to FIG. 8, the control system is operable to activate the catalytic converter heater 45 in response to detection of the activation point during the start up phase of the internal combustion engine. However, the control system 26 could also be responsive to detection of other operating phases of the internal combustion engine in which the catalytic converter is not at its working temperature, for example when the internal combustion engine is switched off and the electric motor is driving the wheels in a situation, for example, where operating parameters suggests that internal combustion engine power is then needed. An example of such a situation could be, for example, where the battery power for electric motor only operation is getting low and the battery 40 needs to be recharged. This would enable the internal combustion engine to operate with maximum efficiency and to get the catalytic converter back up to temperature as quickly as possible.

FIG. 9 is a chart comparing an example of catalytic converter temperatures over time with and without the application of an external load. The upper curve 70 illustrates the heating of the catalytic converter with the externally applied load and the lower (dashed) curve 72 illustrates the heating of the catalytic converter without the externally applied load.

FIG. 10 is a chart illustrating an example of an improvement in the increase of catalytic converter temperature over time. FIG. 10 illustrates the beneficial result that within the first ten seconds, an improvement in the increase in temperature of the order of 50% to 100% can be achieved with the use of the external load compared to not applying the external load.

Thus there has been described a method and apparatus that can increase the rate at which a catalytic converter of an internal combustion engine heats up to its normal operating temperature range by applying an electrical load that is powered by the internal combustion engine during a start up phase. Applying the electrical load demands more power from the internal combustion engine which therefore has to work harder to maintain a given engine speed. The internal combustion engine therefore generates more heat that can be used to reduce the time to bring the catalytic converter up to its working temperature. As a result, a reduction in emissions can be achieved.

Although the embodiments above have been described in considerable detail, numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications as well as their equivalents. 

1. A method of operating an engine system, the engine system including an internal combustion engine that is operable to apply drive to a drive train, a catalytic converter through which exhaust gases from the internal combustion engine pass and a control system, the method comprising: determining, by the control system, that the internal combustion engine is in an operating phase in which the catalytic converter is not at its working temperature; and activating, by the control system, an electrical load element that is powered by the internal combustion engine so that an additional load is placed on the internal combustion engine in response to said determining by the control system.
 2. The method of claim 1, wherein the engine system comprises a generator driven by the internal combustion engine, the electrical load being powered by the internal combustion engine via the generator.
 3. The method of claim 1, wherein the engine system includes a battery, and wherein the electrical load draws a current in excess of that available from the battery.
 4. The method of claim 1, wherein the electrical load is a catalytic converter heater.
 5. The method of claim 4, wherein the catalytic converter heater is integral to the catalytic converter.
 6. The method of claim 4, wherein the catalytic converter heater is external to the catalytic converter.
 7. The method of claim 1, wherein the additional load is applied until the catalytic converter reaches a predetermined temperature.
 8. The method of claim 1, wherein the additional load is applied until the catalytic converter reaches a predetermined temperature or until a predetermined time has elapsed, whichever occurs first.
 9. The method of claim 1, wherein the additional load is applied for a predetermined time.
 10. The method of claim 1, wherein the operating phase of the internal combustion engine is a start up phase.
 11. An engine system comprising: an internal combustion engine that is operable to apply drive to a drive train; a catalytic converter through which exhaust gases from the internal combustion engine pass; and a control system operable to determine that the internal combustion engine is in an operating phase in which the catalytic converter is not at its working temperature, and then to activate an electrical load element that is powered by the internal combustion engineso that an additional load is placed on the internal combustion engine in response to the determination by the control system.
 12. The engine system of claim 11, comprising a generator driven by the internal combustion engine, the electrical load being powered by the internal combustion engine via the generator.
 13. The engine system of claim 11, wherein the engine system includes a battery, and wherein the electrical load draws a current in excess of that available from the battery.
 14. The engine system of claim 11, wherein the electrical load element is in the form of a catalytic converter heater.
 15. The engine system of claim 14, wherein the catalytic converter heater is integral to the catalytic converter.
 16. The engine system of claim 14, wherein the catalytic converter heater is external to the catalytic converter.
 17. The engine system of claim 11, wherein the control system is operable to apply the additional load until the catalytic converter reaches a predetermined temperature.
 18. The engine system of claim 11, wherein the control system is operable to apply the additional load until the catalytic converter reaches a predetermined temperature or until a predetermined time has elapsed, whichever occurs first.
 19. The engine system of claim 11, wherein the control system is operable to apply the additional load for a predetermined time.
 20. The engine system of claim 11, wherein the operating phase of the internal combustion engine is a start up phase.
 21. A motor vehicle comprising an engine system, the engine system comprising: an internal combustion engine that is operable to apply drive to a drive train; a catalytic converter through which exhaust gases from the internal combustion engine pass; and a control system operable to determine that the internal combustion engine is in an operating phase in which the catalytic converter is not at its working temperature, and then to activate an electrical load element that is powered by the internal combustion engine so that an additional load is placed on the internal combustion engine in response to the determination by the control system.
 22. The motor vehicle of claim 21, comprising the electrical load element is in the form of a catalytic converter heater.
 23. The motor vehicle of claim 21, wherein the operating phase of the internal combustion engine is a start up phase.
 24. The motor vehicle of claim 21, wherein: the motor vehicle is a hybrid vehicle that also includes at least one electric drive motor; and the operating phase of the internal combustion engine is one of a start up phase and an electrical drive phase.
 25. A method of controlling an engine system having an internal combustion engine and a catalytic converter, the method comprising: determining that the catalytic converter is not within a predetermined operating range of temperature; based on said determining, activating a heater of the catalytic converter so that an additional load is placed on the internal combustion engine; drawing power away from the internal combustion engine to provide power to the activated heater while maintaining an engine speed of the internal combustion engine; and heating the catalytic converter with heat provided from both the heater and the internal combustion engine at least while the additional load is placed on the internal combustion engine. 